Field of the Disclosure
The present disclosure relates to the field of power electronics, and more particularly, to an LED drive circuit.
Background of the Disclosure
In order to minimize LED drive circuits, LED loads are usually integrated together with a low dropout (LDO) linear voltage regulator to directly receive a rectified half-wave signal for driving the LED loads.
FIG. 1 is a circuit diagram of an LED drive circuit according to the prior art. As shown in FIG. 1, a plurality of LED loads D1 to D4 are coupled in series between a high-voltage terminal and low-voltage terminal (i.e., the ground terminal in FIG. 1) of an input port. A plurality of transistors S1 to S4 are respectively coupled to a cathode of a corresponding LED load and the ground, and an input voltage is a rectified half-wave signal. When the input voltage is low, the transistor S1 operates in a linear state such that the LED loads D2 to D4 are short-circuited, and meanwhile the transistor S1 can regulate the current flowing through the LED loads in accordance with actual requirements. When the input voltage rises, the transistor S2 operates in the linear state such that the LED loads D3 to D4 are short-circuited and the transistor S2 can regulate the current flowing through the series circuit consisting of the LED loads D1 to D2, and so on. FIG. 2 is an operating waveform diagram showing variation of the input voltage and operating states of the transistors. In the technical scheme shown by FIG. 1, during each operating cycle, the LED load D1 has the longest operating time, and the LED load D4 closest to the ground has the shortest operating time. On one aspect, uneven use of LED loads will reduce the lifetime of the whole circuit, on the other aspect, the absolute usage time of the LED loads is shortened, resulting in low utilization of the LED loads.